1. Field of the Invention
This invention relates to home security systems capable of distinguishing intruders from permitted occupants and methods of operation for the same.
2. The Prior Art
The use of both Doppler and non-Doppler ultrasonic and electromagnetic detection systems is well known.
Bolger, "Doppler Correction Radar Providing Combined Target Detection and Ranging", U.S. Pat. No. 3,882,494, is directed to a ranging type device which provides for the transmission and reception of signals to provide a signal from a moving target. The observer listens for an audio frequency which is indicative of the Doppler frequency signature of a moving target within a course/range subinterval. The presence of a moving target is detected as a low volume, Doppler frequency, signature signal. The fine range of the target is then selected in a particular range bin which results in a Doppler frequency signature signal. Bolger requires the active intervention of a human operator in the distance determination.
Greer, "Magnetic System for Discrimination Between Vehicles and Personnel Based upon their Characteristic Frequency Signatures", U.S. Pat. No. 3,889,181, is directed to a system which includes a low pass and a high pass filter adapted to pick up personal magnetic signatures on one hand, and vehicle magnetic signatures on the other. Greer performs his detection and classification function on the basis of signal amplitude and frequency content. Classification on the basis of frequency content is possible by virtue of spectral characteristics which differ between vehicles and personnel magnetic signatures. Personnel, carrying metallic objects, generate frequency on the order of a few tenths of a Hz., while vehicles generate frequencies from a few tenths of a Hz. to more than one Hz. Because of the overlap between vehicle and personnel magnetic signatures, higher frequency components, arising from the rapid mechanical motion of various mechanical vehicular parts, are detected to make the distinction between personnel and vehicles. The bandwidth for vehicular motions of this type are in the range of 6 to 40 Hz. By designing a system to process these two frequency ranges, a highly effective classifier is realized since personnel will generate signatures only in low frequency ranges, and vehicles will always generate signals in both ranges. Greer does not memorize a characteristic range of signatures, but simply looks to signals at various spectral subintervals. Greer's system, for example, has no capability of distinguishing a normal movement from an abnormal one, as is necessary for an alarm.
Gershberg et al., "Ranging Quadrature Doppler Microwave Intrusion Alarm System", U.S. Pat. No. 4,286,260, shows an intrusion alarm system which includes signal channels for quadrature processing wherein different types of sideband techniques are used to enhance what are termed legitimate and true signals over false alarm signals. Gershberg's alarm system attempts to control the effective range of the intrusion alarm system to minimize nuisance alarms caused by targets moving outside of the desired protected area. Ranging, according to Gershberg, is achieved by establishing a time window within the system which responds to a returning echo. Any signal received outside this time window is rejected by the system. The time window is established such that a target within a specified range limit will return an echo before the time window expires. The signal is subject to quadrature and processing to discriminate against double sideband signals produced by vibrating reflective objects, and to enhance the single sideband signals produced by intruders within the specified range limit. Thus, Gershberg has a discriminating circuit which identifies abnormal signatures over normal ones by processing the transmitted and received signal to limit the geographic range of the intrusion. Gershberg is not capable of distinguishing allowable moving masses from intruders.
Nakauchi, "Surveillance System in which a Reflected Signal Pattern is Compared to a Reference Pattern", U.S. Pat. No. 4,382,291, uses an ultrasonic element controlled by a transmitter circuit. The ultrasonic waves from ultrasonic element 1 are reflected by various objects and received again by the ultrasonic element. The reflections are converted into digital signals by circuit 3 and transmitted to the operation processing circuit 4. The operation processing circuit 4 prepares a reference pattern in advance based on patterns and reflections collected by receiver circuit 3. When the area under surveillance is monitored, the pattern of reflections responsive to conditions in the area under surveillance is then compared to the reference pattern. When the two patterns are different, operation processing circuit 4 energizes alarm 5.
Although Nakauchi specifically refers to ultrasonic waves in the illustrated embodiment, electromagnetic waves and optical energy are suggested for alternative detection beams. Nakauchi is not capable of allowing normal, allowable movement without energizing alarm 5.
Follen et al., "Intruder Detection System", U.S. Pat. No. 4, 197,537, is another example of a system which senses, stores and compares sense signals against a reference. Follen particularly uses a microwave radiation which is spherically radiated from a single point source into space to illuminate or "paint" a secured area with a narrow ring of radiated energy of growing radius. As the radiated energy intersects objects in the predetermined range, signals are reflected back to a receiver and converted into a signal pattern representing the reflected pattern within one or more range rings of the secured area. The reflected pattern of the area, or a selected portion thereof, establishes a norm, which is recalled and periodically compared with future signals from the same area. A special automatic gain control and sign processing circuit establishes an ambient or reference signal, and this circuit in combination with comparison logic provides a basis for future signal comparison. Follen's system thus operates without generating nuisance alarms in an environment where objects, although locally fixed, exhibit limited motion. Any movement greater than a predetermined allowable limited movement, whether "normal" or "abnormal", would generate an alarm signal in Follen's system.
Terrell et al., "Electromagnetic Intrusion Sensor", U.S. Pat. No. 4,054,871, is directed to a Doppler type electromagnetic intrusion sensor. The signal is generated in transmitter 10 and a portion of the signal is then reflected from target 20 and returned to the receiver. The reflected signal 24 is then mixed with the transmitted signal 22 and when target 20 is in motion a Doppler signal is produced. This signal is amplified, filtered and fed into a signal processor 18 which produces an alarm output 19 when information indicates the presence of an intruder. Terrell shows the general concept of a Doppler type radar, giving an alarm signal responsive to an abstract signature comparison. Terrell detects moving objects, but does not have the ability to distinguish allowable moving objects from intruders.
Galvin, "Ultrasonic Intrusion Alarm", U.S. Pat. No. 3,665,443, exploits the phenomenon that the spectrum caused by an interfering phenomenon, such as air turbulence, is symmetrically arranged about the carrier frequency of the transmitted signal. The spectrum and the signal attributable to an actual target is in contrast asymmetrical with respect to the carrier frequency. If the spectrum of the received target is unbalance by a predetermined amount with respect to the carrier, an alarm will be produced.
Johnston, "Radar Target Identification System", U.S. Pat. No. 3,733,603, shows an automated recognition computer 13 connected to line 2. Computer 13 is coupled to a display device 14. Johnston indicates that vehicles may be discriminated from other targets due to differences of the scintillation frequencies and body motion frequencies of the objects. Echoes from radar targets have been found to be modulated in amplitude as a result of three types of target motion, normal trajectory motion, body motion and other motions. Trajectory motion is due to aeroballistic effects and missile attitude programming. Body motions include the effects of wind gusts, guidance maneuvers, corkscrewing, nutation and the like. "Other effects" is meant to include missile spin, effects of air brakes and configuration changes. All of these phenomena represent radar signatures indicative of missiles. The above modulations or scintillations of radar signals can be processed and appropriately utilized to obtain useful target identification. Although Johnston is not simply identifying "an intruder" but is capable of discriminating a normal intruder from an abnormal one, this identification is based upon repeatable and distinguishable frequency differences in a very narrow class of targets, namely missiles in flight.
Buckley et al., "Intruder Detection Device", U.S. Pat. No. 4,028,690, is directed to an electromagnetic intrusion system in which the receiver signal is sensed at predetermined intervals of time, and an alarm is initiated only when a change in any one of the predetermined intervals exceeds a predetermined amount. As a consequence, permanent changes in signal level are insufficient to cause a comparative output and are effectively removed over a period of time. Such small changes can be caused by slow alterations of the transmitted signal, or may arise from environmental reasons such as temperature changes or weather conditions which alter the attenuation of the signal path. However, signal changes caused by intrusion of the human being into the protected zone, consisting of an area between the transmitter and receiver, tend to be of a greater magnitude and of shorter duration than those occurring due to environmental causes. Thus, Buckley generally shows an electromagnetic intrusion system in which the reference signal discriminates slow-moving or slowly changing intruders as normal against more quickly moving intruders as abnormal.
What is missing from each of the references, singly and in combination, is any type of apparatus or methodology which is capable of retaining a time dependent reference template which contains information concerning moving objects, as well as stationary objects, within a monitored area.
Home security systems of the type using the technology disclosed in the references are, therefore, limited by their inability to distinguish between a normal, acceptable moving presence and a non-acceptable moving intrusion in a monitored area.
In a typical home there is constant movement. Members of the family, pets, delivery men and others are all expected to move about the house in certain areas at certain times.
Any security system was heretofore incapable of distinguishing the aforementioned acceptable and normal household activity from abnormal movement which would indicate an unknown and unwanted intruder's being present in a given area. For instance, in a family consisting of a 190-lb. father, a 120-lb. mother, a 70-lb. child and a 30-lb. dog, the presence of a 165-lb. moving object in the living room at 3:00 a.m. should be determined by a security system to be an abnormal presence which would cause an alarm condition to exist. However, the presence of the family dog in the living room at 3:00 a.m. should not warrant the sounding of an alarm.
As shown in the previous example, a security system which can distinguish between normal, acceptable movement and abnormal movement would be of tremendous benefit. Such a system would not sound a "false alarm" in the event of normal and allowable movement within a monitored area. The savings in time and money of not having to respond to "false alarms" are numerous and obvious.
Thus, there is a need for a home security system which instantly and automatically determines that an object (intruder) is present in a given area.
There is further need for such a system to distinguish between a normal authorized moving presence and an abnormal unauthorized intrusion.
There is further need for such a security system which can communicate with outside systems, such as alarms, to notify and/or alert the appropriate system or person to take appropriate action if an unauthorized intrusion occurs.